Wendy won't be serving you breakfast, but Ronald might offer it all day.

McDonald's is considering putting breakfast on the all-day menu, not long after Wendy's earlier this year ended its national breakfast experiment. Breakfast accounts for 25% of McDonald's business and has been one of the biggest opportunities for the restaurant industry -- the only area of growth in the past decade, according to NPD. And consumer trends in food, including the desire for speed, convenience, portability and more-healthful, fresher options, are driving chains such as Denny's and even Pinkberry to cash in on the $50 billion restaurant-breakfast category.

So why couldn't Wendy's make breakfast work? It wasn't for lack of effort: The fast feeder has tried the meal a number of times. But breakfast-eating habits tend to be habitual, and Wendy's was late to the daypart.

"They just moved too little, too late," said Elizabeth Friend, consumer-food-service analyst at Euromonitor International. "McDonald's had already done such a good job claiming that share of breakfast," she said, noting that chains like Starbucks also expanded their breakfast products.

Chief Financial Officer Stephen Hare told investors recently that the chain made a serious effort last year. "We really charged into breakfast saying, "Look, we're the only major hamburger chain in QSR that's not a participant in the breakfast category.'"

A spokesman said Wendy's will continue to offer breakfast at the 300 to 400 locations where it's been successful (it has 5,800 U.S. locations). Mr. Hare noted that Wendy's weakness may have been the absence of a strong coffee product, but the chain maintains that its Redheaded Roasters brand can be successful in all dayparts. (About $18 billion of restaurant-breakfast sales comes from hot beverages, according to Technomic.)

In a recent CNBC interview, McDonald's CEO Don Thompson said that the chain is considering offering breakfast all day, but a spokeswoman said that nothing is definite.

Even without all-day breakfast, McDonald's has dominated the daypart since it introduced the Egg McMuffin 40 years ago. "The morning consumer is very driven by habit," said Noelle Laughter, director-marketing, McDonald's USA. "It's about appealing to the consumer need in that time frame."

McDonald's has revamped its coffee in recent years with McCafé; rolled out oatmeal (which is offered all day) and this spring introduced its first breakfast sandwich in 10 years: the 250-calorie Egg White Delight (50 calories fewer than the standard Egg McMuffin) to attract health-conscious consumers.

Taco Bell, Burger King and Subway are also focusing on the daypart: Subway rolled out its breakfast line in 2010 and recently offered an all-day breakfast as part of its monthly "$5 Footlong" promotion.

Breakfast sandwiches play into the growing popularity of sandwiches at restaurants, and they account for much of the breakfast-traffic boost. In the year ended February 28, 46% of all breakfasts bought at a restaurant included a sandwich, compared with 44% a year earlier, according to NPD. In 1989 it was 23%.

Fast feeders, of course, have benefited from convenience and portability trends. But they're not the only ones trying to cash in. "Everyone is going after it, even if it wasn't something they considered before," said Ms. Friend, citing frozen-yogurt chains like Pinkberry.

Traditional full-service diners like Denny's and IHOP are searching for ways to introduce a quicker breakfast. "IHOP is also exploring innovations [that will serve] our on-the-go guests," said an IHOP spokesman. Those include "leveraging new technology to reduce time to order and pay, [and] nontraditional IHOP formats," including a fast-casual concept.

"You can have the 1950s breakfast to go now," said NPD Group VP Harry Balzer, noting that the average time spent eating breakfast is 13 minutes.

Indeed you can -- or at least you can come close. Denny's fast-casual concept, Fresh Express, which has about a dozen locations at airports, universities, hospitals and food courts, offers the Grand Slam sandwich, a portable version of its signature Grand Slam breakfast dish.